The Reds top scorer was forced to miss this afternoon's goalless Barclays Premier League draw with Fulham because of the problem.

It is a worrying development for the Reds, who had hoped the Spain international's discomfort was not serious.

Torres, 26, was sidelined for a month after a knee operation in January.

Manager Rafael Benitez said: "He has a problem with his knee and has gone to see a specialist. We are waiting for news.

"We don't know really, it depends on the specialists tomorrow.

"He had a problem before and we were trying to protect him."

Benitez attracted howls of derision when he controversially substituted Torres with 25 minutes remaining at Birmingham last week with the score 1-1.

But the manager insisted the player was tired and needed ice treatment on his knee.

Torres recovered sufficiently to play, and score twice, in Thursday's Europa League quarter-final win over Benfica but again left the field early.

Liverpool are next in action when they face West Ham at Anfield a week on Monday.

They then face Torres' former club Atletico Madrid in the first leg of their Europa League semi-final three days later.